1. Field of the Invention (Technical Field)
The methods and apparatuses of the present invention are to be used in providing systems for cool thermal storage, either long term storage such as seasonal storage or short term storage such as day by day storage. Some of the systems can also be used to accomplish purification of dilute aqueous and non-aqueous solutions.
The current market for cool thermal storage is created by electric utilities. The benefits derived by the utility may include increased revenue, lower cost production, or shifting summer demand. Electric utilities supplement persuasive marketing programs with attractive utility rates to sell the cool thermal storage concept. Many utilities will contribute cash rebates on the basis of "Avoided demand" for thermal storage systems.
Electric utilities generate power from several different energy sources with energy cost ranging from low cost hydro and nuclear to expensive gas turbines. Many lower energy cost nuclear and hydro plants have excess capacity during off-peak hours (typically 9 pm to 9 am), while the cost of operating gas turbines for peaking often exceeds revenue from the power they generate. Lowering on-peak daytime demand and increasing off-peak nighttime demand enhances utility profitability. Load management just makes good economic sense. Cool thermal storage contributes to improved load management. The capital cost of cool thermal storage systems can be offset by utility savings passed on to the owner. The vehicle to pass on savings may be high daytime demand charges that are waived during off-peak hours, discounts for off-peak power or cash rebates for comfort systems that move the power requirements from on-peak hours to off-peak hours.
A system of the present invention may serve as a dural purpose system for cool storage and water purification. It is particularly effective in treating dilute solutions. Polluted waters containing toxic pollutants in low concentrations are produced from various sources, such as underground waters, industrial waste waters and nuclear waste waters. Such waste water can be treated to produce usable water. A dual purpose system has tremendous advantages over conventional cool storage systems and conventional water purification systems.
2. Background Art
Since a dual purpose system of the present invention can provide both cool thermal storage and water purification, prior art on cool thermal storage and water purification by vacuum freezing are reviewed in the following:
Cool Thermal Storage
Chilled water, ice, or other phase change materials can be used as a cool storage medium. Prior art on chilled water storage, ice storage and eutectic hydrate salt storage is outlined.
Chilled Water Storage
Conceptually, chilled water storage appears to be a simple design. Water stores heat by increasing its temperature. The specific heat of water is one Btu per degree Fahrenheit per pound. 12000 degree Fahrenheit pounds are required to store one tonhour of cooling. Chilled water storage is traditionally designed on a 20 degree Fahrenheit temperature rise, which equates to almost 10 cubic feet of water per tonhour. Chillers have very little difficulty cooling water to the minimum design temperature, typically 40.degree. F.
Chilled water at around 4.5.degree. C. (40.1.degree. F.) may be produced by absorption refrigeration or mechanical compression refrigeration. Major manufacturers of absorption refrigeration machines are Carrier Corporation of Syracuse, New York and Trane Company of Le Crosse, Wis. Major manufacturers of mechanical compression water chillers are York Company of York Pennsylvania and Trane Company of Le Crosse, Wis. An absorption chiller usually uses a lithium bromide-water mixture as the working medium. A mechanical chiller uses a centrifugal compressor, screw compressor or reciprocating compressor and Freon as the refrigerant.
Ice Storage
The latent heat of fusion or the heat absorbed by one pound of ice when it melts is 144 Btu. This equates to less than 1.5 cubic feet of ice per tonhour. There are three types of conventional systems of ice storage. These three types are: (a) static ice storage, (b) dynamic ice storage and (c) slush ice storage. It will be shown that the present invention introduces several new types of ice storage systems.
Static Ice Storage Systems
In a static ice storage system, ice is made on tubes by an indirect freezing operation and is melted in place by circulating water to thereby produce chilled water for air conditioning. The volume of ice must be permeated with channels of fluid to transport heat into and out of the body ice. The fluid in the pipe can be brine or refrigerant. Brine systems use ethylene glycol to transport heat into and out of the ice. Refrigerant systems circulate refrigerant through the pipe to remove heat from the tank, but circulate water through the pipe or through the free area around the ice when adding heat to the tank.
A major manufacturer of static ice storage systems is CALMAC Manufacturing Corporation of Englewood, N.J. CALMAC Corporation uses water chillers manufactured by Trane Company in its ice storage systems.
Dynamic Ice Storage Systems
In a dynamic ice storage system, ice is produced by a flake ice machine and flake ice is stored in a vessel stream of circulating water is brought in contact with flake ice to be chilled and returned for cooling process equipment or a building. Major manufacturers of dynamic ice storage systems are Turbo Company of Denton, Tex. and Mueller Company in Springfield, Mo.
Slushy Ice Storage Systems
In a slushy ice storage system, a slushy ice mixture is formed by an indirect freezing operation. A mass of slushy ice may be directly circulated for air conditioning or a water stream may be chilled by the slushy ice and used for air conditioning. Developers of slushy ice systems are Chicago Bridge and Iron Company in Chicago, Ill. and Sunwell Engineering Company in Canada.
Eutectic Mixtures of Hydrate Salts
Eutectic mixtures of hydrate salts that solidify and melt in the range of 5.degree. C. to 15.degree. C. (41.degree. F. to 59.degree. F.) have been used to provide cool storage. A hydrate crystal has host molecules with many molecules of water around each host molecule. For example, Dow Chemical Co. has introduced a mixture based on calcium chloride hexahydrate and calcium bromide hexahydrate. The mixture has a transition temperature around 14.degree. C. (58.degree. F.). A eutectic mixture of hydrates can be used to store coolness at a temperature higher than an ice storage system and therefore saves energy. Transphase Systems, Inc. of Huntington Beach, Calif. is a major supplier of eutectic cool storage systems.
Vacuum Freezing Processes
Referring to the processing of an aqueous solution by any vacuum freezing process, the aqueous solution is introduced into a chamber which is maintained at a pressure that is somewhat lower than the vapor pressure of the solution at the freezing temperature of the solution to thereby simultaneously flash vaporize water and form ice crystals. This operation is referred to as S/L/V multiple phase transformation in a vacuum freezing process. As the result of this operation, a low pressure water vapor, referred to as a first vapor, and an ice-mother liquor slurry, referred to as a first condensed mass, are formed. In the case of sea water desalination, this pressure is around 3.5 torr. The low pressure water vapor formed has to be removed and transformed into a condensed state; the ice crystals have to be separated from the mother liquor; the resulting purified ice has to be melted to yield fresh water. Furthermore, the heat released in transforming the vapor into a condensed state has to be utilized in supplying the heat needed in melting the ice. The processes to be described utilize different ways of vapor removal and different ways of accomplishing the heat reuse.
Several vacuum freezing processes have been introduced by workers in the desalination field. These processes are (1) Vacuum Freezing Vapor Compression (VFVC) Process, developed by Colt Industries, and described in the Office of Saline Water, Research and Development Report No. 295, (2) Vacuum Freezing Vapor Absorption (VFVA) Process, developed by Carrier Corporation, and described in the Office of Saline Water, Research and Development Report No. 113, (3) Vacuum Freezing Ejector Absorption (VFEA) Process, developed by Colt Industries, and described in the Office of Saline Water, Research and Development Report No. 744, (4) Vacuum Freezing Solid Condensation (VFSC) Process developed in the Catholic University of America, and described in the Office of Saline Water, Research and Development Report No. 511, (5) Absorption Freezing Vapor Compression (AFVC) Process, introduced by Concentration Specialists, Inc., and described in the report submitted to the Office of Saline Water, (6) Vacuum Freezing High Pressure Ice Melting (VFPIM), introduced by Chen-Yen Cheng and Sing-Wang Cheng, and described in U.S. Pat. No. 4,236,382 and (7) Vacuum Freezing Multiple Phase Transformation Process, also introduced by Chen-Yen Cheng and Sing-Wang Cheng and described in U.S. Pat. No. 4,505,728.